Top silo unloaders are suspended from a tripod which is supported upon the top of the silo wall and extends into the domed silo roof. Those silo unloaders which have a drive ring are provided with three horizontal support arms the outer ends of which are outside the perimeter of the drive ring, and suspension cables which are trained over sheaves in the upper part of the tripod are secured to the outer ends of the support arms so that the silo unloader may be moved vertically in the silo by operation of a winch near the base of the silo.
When a silo is to be filled, the unloader must be raised high enough to avoid or minimize interference with the incoming material.
If the silo unloader is too low some of the incoming material will drop onto the cutter-conveyor pickup arm and other components. This results in severe overloading of the supporting tripod and can cause damage to or collapse of the tripod. In addition, these lower silo unloader components will intercept or deflect the incoming silage stream and thus prevent the desired even and symmetrical placement of material across the entire area of the silo.
The silo unloader discharge chute may be removed; but even so the vertical height of the unloader and the span across the support arms usually prevents raising the unloader high enough to prevent the pickup arm from interfering seriously with the incoming material.